Drilling fluids



all)

'! Claims.

the bit, washes over the cutting faces of the bit, and rises to the surface through the annular s yionuunskd is;

space surrounding the drill pipe, this annular...-

space approximating the amount by which the diameter or" steil. There are two essential characteristics or oil well drilling muds required to accomplish two more or less distinct 1 ens. One characteristic required is that the mud contain a material which will effectively seal the walls or the open hole made and homogeneously s the cuttings which pass from the bit upwarthrough the annular spaces surrounding the drill stem at times when the pumps are not circulating the mud. There are a number of other effects obtained from a good wall building mud which have previously been discussed. The second requirement for an oil well mud very often is that the mud have a weight per unit volume considerably in excess of the weight of water in order the hit exceeds the diameter of the r to produce a head resistant to unusual gas or water pressures encountered during boring, to assist in forcing wall cuildin mud into formations for better sealing characteristics.

The accomplishment of these two requirements for an oil well drilling mud is in many instances co-mingled; for example, in the present art, if a mud is to be weighted to 12 pounds per gallon, material under the first classification must be available in the mud to homogeneously support the weighting material as well as the cuttings. The greatest part of the weighting material used at the present time in the art consists of either finely ground barytes or iron oxide, both of which have strong settling tendencies. For purposes of clarity in this specification we will term mud re quiremcnts oi the first classification gel-type, and rccuireiiients oi the second classification wcig' iting-type.

An object of this invention is to provide a new and improved weighting ty e of drilling mud and in combination with this a no and improved geltype mud. ther objects will appear hereinafter.

The ideal weighted drilli g mud is one in v. the in: mum \x'eig'ht per go. i can he with a minimum rise in viscos' y.. press greatly in excess of hydrostatic head pressures have been encountered in many formations. The following table demonstates the rapid increase in pressure per sciuare inch for comparatively small additions to the weight of one gallon or mud.

TABLE I Hydrostatic head in a typical well 10,000 feet deep The weighting materials used in the present iron oxide and cai'ytcs, when allowed to settle :er being mixe with water will reach a critical density or between 18 and 19 pounds per gallon. lor example, if a mixture of either of these weighting materials and water, weighing 1; -sounds per gallon, is allowed to stand for apiately 48 hours, the settled portion of the weighting material left after decanting the superwater will have a density oi between 18 and 19 pounds. The addition of gel-type material to such a mixture will decrease the density of the settled material, but to accomplish the complete suspension of the material it is necessary to maize such a viscous mass that its use would not be practical in an oil well. For example, a brine gel was made containing 5% of brine gel material treated with 5% of its dry weight of lime, and there was added finely ground weighting material. The mixture was thoroughly agitated. The resultant viscosity was 86 centipolses and the weight per gallon was 13.1 pounds. The maximum desirable viscosity for practical use apiroximates 4O centipoises. After settling for 24 hours the weight of the settled material was 14.6 pounds per gallon. Similar tests showed that the weight of an ll-pound mud increased to a 12.5- pound settled mud. It is characteristic of these materials that the most dense settling takes place at the bottom of column, which in an oil well tends to sticl; the bit. Thus, it is evident that in drilling practice with heavy muds the rate of circulation must be considerably depended upon to prevent settling in the hole. In many instances drills have been stucl-z when the circulation, for one reason or another, has been shut down for a 1 of time. Rirthermore, when the mud has art, 1.

found that the weighting material settles out to a considerable extent, falling to the bottom of th pit along with the heavier cuttings that are being discarded. The refuse is customarily jetted out of a settling pit into a discard pit and it is obvious that a considerable amount of weighting material goes into discard in this way. In actual practice it is often necessary to use two or three times the amount of weighting material which would be necessary to make the mud to fill the hole and the pits provided none of the weigh ng material were discarded. In addition to tins, is often true that where a mud weighing more than 11 or 12 pounds per Jbn is so viscous and contains so much solid that it impossible to drop the cuttings brought up from the bottom of the hole, it is causing increased wear on the couip mt and defeating the purpose of the settling p; s.

Our present invention eliminates all or these difficulties besides providing new advantages for the mud. We have found that oy adding to oil well drilling fluids a water-soluble heavy metal salt or a combination of salt which are soluble in water, it is possible to increase the weight of 1... drilling fluid without the necessity of adding a suspended type of solid weighting materiel such as is now used in the art. We have found that where single soluble heavy metal salts are added for weighting purposes, a salt, which when dissolved in water at ordinary temperatures will fOllll a solution of minimum speci 1c gravity of 1.4, is desirable, it being thus possl ole to in rease the weight of drilling fluid much more than that of normal fluid and into the range of what may called heavy drilling fiuids, for instance, more than 11.5 pounds per gallon wmght.

We have found that there is consderable economic advantage in melting heavy drilling fluids by the use of more than one alt in the sol There is also a great technical in this procedure. We ha und, 1 instance, that to a. sat" "ated solson; :1 chloride, zinc chloride may be continuously added t ordinary temperatures to an extent 55% by weight or" the total solution without precipitating either salt. Also, zinc chloride can be added to a saturated solution of calcium chloride to a very considerable extent without precipitating either salt.

The following table illustrates the pr portions of water, sodium chloride, and zinc chloride, as well as the proportions of water, calcium chloride, and zinc chloride with the respective specific gravities, and weights per gallon of these solutions, required to produce a certain total wei ht per gallon.

T \BLE .Ll.

Composition of solution (by wt.)

Total Water NoOl CaCl; ZnCh Sp. wt. pct

grov. go].

Lb../ Lbs} Lbs./ Lbs I gel. 0 gal. gel. gel.

75. O 7. iii] 25. 0 2. 50 0 0 9. 96 d7. 7 T. M 22. 3 2. 35 1. 05 1o. 5 to. o s. or; no. 0 2.21 2. :1 ll. o (11, 5 ll. 27 17. 5 2. (l0 3. 5'.) ll. 45.0 5. 15.0 1.. -i() 5.15 12. 7 157. I 5. .5 l2. 5 1. L0 7. 06 l- 11 (-0. 0 1 0 0 l 5', 0 l0 1. .33 1' 3S 4 0 l0 '2. 6. l. 5.7 l '1 in \r 30 4.13 l. ".0 11 JG. 0 '10 5. 73 1. 7-2 1 133.0 J0 i5 6. GO l. 70 l many other cases, however, it is necessary to weight attai able since an 80% solution of zinc chloride alone will produce a solution or specific gravity 2.25 with a weight of 18.23 pounds per gallon of solution. Other combinations of salts are equally advantageous. For example, there may be added to '70 parts of a saturated solution of sodium chloride, 25 parts of ferrous sulfate to obtain a specific gravity of 1.312. Another example is the addition of 40 parts of ferric sulfate to 60 parts of a saturated solution of sodium chloride to give a specific gravity of 1.49. It is of advantage to use ferrous or ferric sulfate in saturated solution as a base and to add a heavy riot-oi salt such as zinc chloride thereto. An example of ti is the addition or 40 parts of zinc chloride to 63 parts or" ferric sulfate solution to give a specific gravity of 1.66. Solutions containing a combination of sodium chloride, ferric sulfate and zinc chloride are very efficient in imparting weight to a drilling fluid at the lowest cost. The combinations of salt above shown are not intended as limitations on combinations or on single salts, but are intended as concise examples of he practice of this invention.

It will be obvious that heavy solutions disclosed herewith overcome all the difficulties contingent upon the use of insoluble weighting material, now making it possible to' use a heavy drilling fiuid or low viscosity which will quickly drop the cutti gs brought up from the bottom of the hole. There xi-vs placed in the refuse pit may also be accomplished by filtering. In many cases it is of advantage to separate the cuttings from the drilling fluid by means of centrifuging. For example, the specific gravity of the unadulterated drilling may be a value of 2 whereas the cuttings have a specific gravity of 2.5. This type of separation is easily accomplished and may be continuously done by the use of any one of the continuous centrifugal separators now on the market.

In the practice of this invention it is very often the case that a solution of a salt or a combination of salts may be used per so as a drilling fluid. In these cases there is usually a considerable amount of fine material embodied in the fluid by the process of drilling certain formations, and the bull: or this fine material may serve to prevent settiing of the cuttings where the progress of the drilling is fairly steady and the periods during which circulation is stoppedare short. In

produce a gel-type weighted drilling fluid in orde to accomplish the wall sealing, supporting and weighting requirements of the mud. To accomplish this we add to the solution a gel-type clay capable of forming brine gels. A base exchange zeolitic clay as described in our United States Patent No. 2,0-1-i,758 is adaptable for this use. Optionally, a gel can be made with this clay and the soluble salts added afterward. An agent to increase the viscosity and gelling characteristics of the clay may be used. There is no question but what the use of gel-type clay will give superior wall building characteristics to this type of drilling We preferably use 1% to 10% of a base exchange zeolitic clay.

e1 ow v By variations in the concentrations of chloride and zeolitic clay a viscous varying in viscosity from 1 to 80 centipoises wei ing more than 18 pounds per gallon may be cctaincd without the. addition of solid materials such as barytcs, iron oxide, etc.

In many heavy producing; oil districts there occ what is termed heaving shale". For e1:- amplc, the Jackson shale found in the south of Texas is generally termed a heaving shale. There are gradations in the heaving shale. One of these is the bcntonitic type which when hydrated by the drilling mud balls on the bit and forms rings or doughnuts around the drill pipe. This caus the hole to be swabbcd when the bit is raise-d through it, thus destroying the wall. It is many times difficult to raise the bit into the surface casing due to the fact that the ball and doughnut effect sticks at t e bottom of the casing. This shale will heave into the hole, very often stop- :.;tion of tel salts is that insoluble "iting' materials m y be added thereto for a r or increase in wei t per unit volume withou. the undesimble viscosity increase. Ey addins: insoluble weighting material to a i uid partly or wholly ated with soluble salts, a far heavier mud. may now be made than was formerposcibie. in i as, it is now possible to maize roximately double the prcscntweight. apparent that many combinations of weighting materials and insoluble suspendable weighting mate 'ials may be made. or example, dry base weighting material may ""-:ing together 2.2 pounds of pounds of chloride and 2.2 pounds of rinely ground bar tes. This material may be marketed as such and when added to 6.15 pounds of water, will give a mud weighing 12.75 pounds per gallon. Thus, fairly heavy muds may be obtained without undue increase ping circulation of mud, sticking the bit and causing abandonment of the hole. Another type of heaving shale is one which cracks or decrepitates into small pieces when hydrated by the drilling mud and appears at the surface in he mcnclous quantities. This is commonly called buclcshot shale heaves into the hole with the same effect as described above. We have found that drilling fluids comprised of a single soluble 30 heavy metal salt or a combination of salts including a soluble heavy metal salt partially or completely prevent the hydration of decomposition of heaving shales. A variation of shales subjected to a solution of a given salt will show a variation of results. Also, the variation of salts contacted with a given shale will give varyn results. For example, a saturated solution of sodium chlo "ide inactivated or prevented the composing of an Ariola, Texas shale, whereas 40 it did not completely inactivate Matagorda county, Texas shale. However, a combination of zinc chloride and sodium chloride in solution did completely inactivate the latter shale. The addition of various soluble salts to a drilling mud is very important in preventing a shale from heaving.

It is well known in the art of drilling that many formations contain sufficient colloidal matter in the cuttings to seriously thicken the drilling 50 and it is often necessaryto dilute the Furthcr, when a fluid contains a reasonable amount of this type of material it is often'thc case that a viscosity stimulating agent in the formation will suddenly thicken the drilling mud. such instances drilling must be stopped until the mud can be thinned out and got into c sh in viscosity and at a low cost.

T es of other heavy salts that may be used "lg to the teachings herein are ferric sul-/ c chloride, which in 60% solution has a s ecific gravity of 1.63; cadmium chloride, 2 which 66% solution has a specific gravity of into, which in 60% solution has at 1.33; zinc sci specific ravity of 1.45; and tin chloride, which; in 6% solution has a specific gravity of 1.6%. It not intended, however, to limit the soluble salts for use according to these specifications to the specific ones disclosed. The number of soluble salts well adapted to use alone or in combination as disclosed herein is so great that they cannot be conveniently listed. It is intended that the scope of this invention cover the use of soluble reavy metal salts singly; and the use of a combination of two or more soluble salts without reg-rd to their classification as to being heavy metal salts.

The salts or c mbination of salts which we employ in oil well drilling in accordance with this invention often form acid solutions in water. For instance, commercial sodium chloride is slightly acid, calcium chloride more so, and zinc 4o chloride quite acid. The pH may be varied by v'rious combinations of salts.

W e prefer to maintain the pH of the brine solutions as high as is possible without causing preci itation of compounds formed from the salt in the brine. 15y maintaining a drilling fluid on I the alkaline side, corrosion may be greatly prevented. A pI-i of 8 or more is desirable. It is} also desirable, in cases where a tendency to precipitate compounds fro a the salt exists, to add an inhibitor to this action. A buffer salt may o invention ehminates t diff culty due t be added to prevent substantiahvariation of the the fact that muds found informations will not l ion Co centration. It is often necesmalzo a gel or show an increase in viscosity. For to add an 71 nhib to p iiq D esample, bcntonite will not gel when ced in Vent 601T fiion of the q p nt With which the our heavy salt solutions. Thus, our addition oi fluid is usedp s of Such inhibitors ar soluble heavy metal salts to the drilling fluid staar nious oxide and quiholine ethiodide, 11 bilizcs the mud. sun another advantage of our use o about-001w 1 porter either inhibitor per addition of soluble salts is that the accompany- 199 parts of Solution is usually u ficicnt.

ing increase of specific gravity of the solution In the drilling Oil Walls it is 017% (16511" lends power to support cuttings. Thus, t ehomoable to wall the hole more permanently than is gcnoous suspcnsion of the p =rticles in the mud 60 10 y the use Of 1 Sa yp mild. The use 01' o: a well is accomplished with lower visco ity our drilling fluids composed of soluble salts with than is now possible. Furthermore, the fact that certain phosphates, sulfides, silicates, carbo- T0 the heavy solution may be cleaned oi refuse by notes, and oxslates will allow the formation of 1 filtration or centrifuging allows a mud greater cipitate in the interstices oi tv to be used than has been possible hcrc- .to to form a. precipiotncr advantage of our crux" l 1: i w' .2: 1 i oin the zinc chloride oi non suiiate oiine.

Sodium silicate, sodium carbonate and sodium oxalate are other examples of materials that may be used for this purpose. A solution of zinc nitrate and sodium phosphate may be used to form a very hard precipitate.

So much of the present application as relates to oil well drilling fluids prepared iroin waters or b ines and fuller's earth of the l lorida-Gecz's'ii'. type is described and claimed in our eta-pending; application Serial No. 85,334, filed June 5, 1935.

The term "heavy metal as eni l herein covers metals having a specifi gravity greater than four, in accordance with the generally accepted definition given by Hackh, Chemical.- Dictionary, page 3&8, (1929).

Having thus described the invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1'. An oil well drilling fluid containing as a weighting agent a substantial quantity of zinc chloride.

2. An oil well drilling weighted with a suostan'al quantity of zinc chloride dissolved in a saturated sodium chloride solution.

3. An oil well drilling nan. weighted with a su". t chloride dissolved in a saturated solution of calcium chloride.

4. An oil well drilling fluid containing as a weighting agent a plurality of water-soluble salts including substantial amounts of zinc chloride, at least one of said salts being present as a substantially saturated solution in water.

5. An oil well drilling fluid containing a plurality of water-soluble salts, one of which is of the li WY metal group and at least one of which is p 'esent in the form oi a substantiallysaturated solution.

G. the art of earth boring, the step which comprises conducting the drilling operation in the sence of an ac eous salt solution having a s;iec.i.c gravity of from to 2.25, said solution including a substantial quantity of a water soluole salt or nietal whose specific gravity is greater than four.

'7. In the art of earth boring, the step which comprises conducting tne drilling operation in the presence of an aqueous solution having dissolved therein a substantial quantity of a water soluble salt whose specific gravity is greater than "EGY CROSS.

IifllTTHEW FORBES CROSS.

ea in printoi spa-oilicat' on L1 correction follows: Pewe 2 firsst column, line 2o, lor- "suspen suspensoid; and l; "extent" insert the word of; a Column, i 52 f0 1d be read witn thes record of the case ul'fi the same may conform to th ionry Van Ars iale n'OY oB'OSS, 1-1

It is hereby certiiiecl that error appears in printed specification of the above numbered patent requiring correction as follows: first column, line 26, f0

"exten-t,

Page 2; r- "suspended" read suspensoid; and line 44, after insert the word of; and page 3, first column, line 32, for "of" read or; and the said Letters Patent should be read with these correc tions therein that the same may conform to the record of the case in the Patent 0 m signed and sealed this 29th day of June, A. D. 1957.

Van Arsdtale Acting Commissioner of Patents.

March 9, i937. 

